Non-localized acoustic receptivity and subsequent disturbance growth in a Blasius boundary layer

Acoustic receptivity was experimentally examined for a Blasius boundary layer with receptivity sites in the form of 2-D waviness and oblique waviness. Linear receptivity coe cients obtained for all values of forcing combinations ( h) are in good agreement with receptivity theory. The measured receptivity increased markedly with increasing wave obliqueness. Detuning was investigated by varying the streamwise wavenumber, w, of the 2-D and oblique wall waviness. Oblique transition was also investigated by exciting a pair of oblique Orr-Sommerfeld (O-S) modes (f=fo; = w) = (1; 1). For large values of h, a secondary instability was observed that ultimately lead to laminar breakdown. This instability appears to be driven by large spanwise velocity gradients, jdU=d j.